Deposition, carbon

Carbon deposition occurs when EUV photons crack residual hydrocarbons in the vicinity of an EUV optic or reticle. These hydrocarbons may originate from a number of sources such as outgassing of resists or other materials inside the scanner environment, residual air in the exposure chamber, etc. Once deposited, these carbon deposits can be cleaned with minimal or no damage to the underlying multilayer film. This could allow repeated cleaning cycles to be performed to extend the lifetime of an optics system. In this scenario, the frequency and duration of the cleaning procedure could be integrated into the operation of the tool in such a way that acceptable productivity and cost of ownership are maintained.  

The carbon-deposition process of EUV optics has been described to involve adsorption, diffusion, and dissociation of hydrocarbons at the surface of the 

Hollenshead and L. E. Klebanoff, Modeling carbon contamination of extreme ultraviolet (EUV) optics, Proc. SPIE 5374, 675 (2004). 

Hollensheas and L. Klebanoff, ModeUng radiation induced carbon contamination of extreme ultraviolet optics, J. Vac. Sci. Technol. B 24, 64 82 (2006). 

The carbon growth on optics has also been shown to be dependent on the mass of the hydrocarbon contaminant and the partial pressure of hydrocarbons, as well as on the EUV radiation dose and intensity. Experimental results obtained with model hydrocarbon compounds and showing the trends of carbon growth as a function of these parameters are shown in Fig. 14.15. EUV radiation intensity has a pronounced effect on contamination, which appears to initially grow rapidly as the intensity is increased, eventually reaching a plateau. In a similar manner. 

Carbon deposition can also occur on the reforming catalyst and anode in the SOFC via the disproportionation of CO (the Boudouard reaction) (Eq. (8)), and by reduction of CO by H2 (Eq. (22))  

Fipure 12.14 Electron micrograph showingfliainentous carbon growth on a supported nickel catalyst. 

It is clear, therefore, that the problem of carbon deposition and deactivation becomes more severe if bottled gas (propane/butane) is used as the fuel, and more acute still if gasoline or diesel is being contemplated as fuel. To counter the problem of carbon deposition from higher hydrocarbons, a low temperature pre-reforming stage, at 250-500°C, is often employed to remove the higher 

Electrically conducting oxide materials have been investigated as potential anode materials. One of the main attractions of such materials is their resistance to carbon deposition compared to nickel cermet anodes under direct reforming conditions [67,70,74,79,80]. Rhodium, platinum and ruthenium have also 

Sulphur can be removed by various methods. These include high-temperature desulphurisation (hj drodesulphurisation) [3,86-88], whereby sulphur- 

Similar to other techniques of reforming, carbon deposition is the biggest challenge for dry reforming in the presence of nickel-based catalysts. As stated above, platinum and rhodium which are more expensive have shown better resistance to carbon deposition. 

The anode and the reforming catalyst are prone to carbon deposition due to reduction of CO by H2 by the reaction  

In order to determine carbon deposition on the anode and catalyst a new technique has been introduced, temperature-programmed oxidation (TPO). This technique is beneficial in determining a safe operating temperature for avoiding carbon deposition at low oxidant/carbon ratios. The technique allows determining the quantity of carbon deposited on the anode or catalyst with respect to operating time. 

In addition, it helps to determine the temperature at which carbon is removed from the anode thus giving an idea of the interaction strength of carbon with the anode or catalyst material. 

nickel, cobalt, and their alloys are the most studied metals for the catalytic growth of CNFs or CNTs. The readiness of these metals to produce metal-carbon solid solutions and to form metastable carbides in the appropriate reaction temperature range should be an important factor to take into account for the comprehension of their reactivity. The different carbon species formed depending on the temperature range employed in the steam reforming of hydrocarbons on nickel catalysts have been discussed [29] and consist of  

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The properties required by jet engines are linked to the combustion process particular to aviation engines. They must have an excellent cold behavior down to -50°C, a chemical composition which results in a low radiation flame that avoids carbon deposition on the walls, a low level of contaminants such as sediment, water and gums, in order to avoid problems during the airport storage and handling phase. 

In order to maintain high energy efficiency and ensure a long service life of the materials of construction in the combustion chamber, turbine and jet nozzle, a clean burning flame must be obtained that minimizes the heat exchange by radiation and limits the formation of carbon deposits. These qualities are determined by two procedures that determine respectively the smoke point and the luminometer index. 

Scholle, Peter A. et al. (1983) Carbonate Depositional Environments, 708p, AAPG Memoir 33... 

Optional experiment. When all the air has been displaced, collect a test-tube of the gas over water (by appropriate inclination of the end of the delivery tube beneath the mouth of a test-tube filled with water and supported in a beaker of water). Observe the colour and odour of the gas. Ignite the test-tube of gas, and note the luminosity of the flame and the amount of carbon deposited. Pure acetylene is almost odourless the characteristic odour observed is due to traces of hydrides of phosphorus, arsenic and sulphur. 

At Lake Texcoco, Mexico, bicarbonate is available in the alkaline waters from soda ash [497-19-8] (sodium carbonate) deposits (see Alkali and CHLORINE products). This supply of carbon is adequate for growing Spirulina maxima which tolerates alkaline pH values in the range 9—11 (37,38). Combustion gases have been used to grow this organism, but this carbon source is not available in many regions (49). 

Hydrogenation of the oxides of carbon to methane according to the above reactions is sometimes referred to as the Sabatier reactions. Because of the high exothermicity of the methanization reactions, adequate and precise cooling is necessary in order to avoid catalyst deactivation, sintering, and carbon deposition by thermal cracking. 

Naphtha desulfurization is conducted in the vapor phase as described for natural gas. Raw naphtha is preheated and vaporized in a separate furnace. If the sulfur content of the naphtha is very high, after Co—Mo hydrotreating, the naphtha is condensed, H2S is stripped out, and the residual H2S is adsorbed on ZnO. The primary reformer operates at conditions similar to those used with natural gas feed. The nickel catalyst, however, requires a promoter such as potassium in order to avoid carbon deposition at the practical levels of steam-to-carbon ratios of 3.5—5.0. Deposition of carbon from hydrocarbons cracking on the particles of the catalyst reduces the activity of the catalyst for the reforming and results in local uneven heating of the reformer tubes because the firing heat is not removed by the reforming reaction. 

Thermal cracking tends to deposit carbon on the catalyst surface which can be removed by steaming. Carbon deposition by this mechanism tends to occur near the entrance of the catalyst tubes before sufficient hydrogen has been produced by the reforming reactions to suppress the right hand side of the reaction. Promoters, such as potash, are used to help suppress cracking in natural gas feedstocks containing heavier hydrocarbons. Carbon may also be formed by both the disproportionation and the reduction of carbon monoxide... 

A uniform coating of calcium carbonate deposited on the metal surfaces physically segregates the metal from the corrosive environment. To develop the positive LSI required to deposit calcium carbonate, it is usually necessary to adjust the pH or calcium content of the water. Soda ash, caustic soda, or lime (calcium hydroxide) may be used for this adjustment. Lime is usually the most economical alkaH because it raises the calcium content as weU as the alkalinity. 

Theoretically, controUed deposition of calcium carbonate scale can provide a film thick enough to protect, yet thin enough to allow adequate heat transfer. However, low temperature areas do not permit the development of sufficient scale for corrosion protection, and excessive scale forms in high temperature areas and interferes with heat transfer. Therefore, this approach is not used for industrial cooling systems. ControUed calcium carbonate deposition has been used successhiUy in some waterworks distribution systems where substantial temperature increases are not encountered. 

The largest quantity of commercial pyrolytic graphite is produced in large, inductively heated furnaces in which natural gas at low pressure is used as the source of carbon. Deposition temperatures usually range from 1800 to 2000°C on a deposition substrate of fine-grain graphite. 

The heat released from the CO—H2 reaction must be removed from the system to prevent excessive temperatures, catalyst deactivation by sintering, and carbon deposition. Several reactor configurations have been developed to achieve this (47). 

The heat-carrying solids are particles of fluidized sand that circulate between the heating and reaction zones. The reaction section for hght hydrocarbons is at 720 to 850°C (1,328 to 1,562°F), the regenerated sand returns at 50 to 100°C (122 to 212°F) above the reactor temperature. The heat comes mostly from the burning of carbon deposited on the sand. This equipment is perhaps competitively suited to cracking heavy stocks that coke readily. 

Deposits containing carbonate can be protective. The carbonate buffers acidity caused by the segregation of potentially acidic anions in and beneath deposits. However, deposits are rarely composed of only a single chemical mixed deposits are the rule. Deposit morphology also influences attack. Hence, although sometimes carbonate deposits are beneficial, they may also be deleterious. 

Figure 4.16 Thick calcium carbonate deposits on condenser tube and copper transfer pipe. Note the stratification.

The carbon residue is a measure of the carbon compounds left in a fuel after the volatile components have vaporized. Two different carbon residue tests are used, one for light distillates, and one for heavier fuels. For the light fuels, 90% of the fuel is vaporized, and the carbon residue is found in the remaining 10%. For heavier fuels, since the carbon residue is large, 100% of the sample can be used. These tests give a rough approximation of the tendency to form carbon deposits in the combustion system. The metallic compounds present in the ash are related to the corrosion properties of the fuel. 

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